FIG. 13 shows a sectional view of conventional acceleration sensor 5001 disclosed in Patent Document 1. Acceleration sensor 5001 comprises the following elements: mount substrate 61, base glass 62 placed on mount substrate 61, flexible substrate 63 placed on base glass 62, weight 64 placed on a lower surface of flexible substrate 63. Glass substrate 65 is placed above flexible substrate 63 to face flexible substrate 63. Opposed electrodes 66 placed on respective surfaces of flexible substrate 63 and glass substrate 65 facing each other. Weight 64 placed on the lower surface of flexible substrate 63 is movable.
An operation of acceleration sensor 5001 will be described below. An acceleration applied to sensor 5001 urges weight 64 along the direction of the acceleration, and causes flexible substrate 63 having weight 64 attached thereon to warp, thereby displacing flexible substrate 63. This displacement changes the distance between flexible substrate 63 and glass substrate 65, accordingly changing a capacitance between opposed electrodes 66. The sensor detects the acceleration based on the change in the capacitance due to the change in the distance between electrodes 66.
Acceleration sensor 5001 is oriented along the direction of the acceleration to be sensed in an attitude control device or a navigation system of mobile carriers, such as vehicles.
Acceleration sensor 5001 detects the acceleration based on the change in the capacitance between opposed electrodes 66. Weight 64 is placed on the lower surface of flexible substrate 63 and located above away from mount substrate 61. This arrangement causes weight 64 to be displaced easily in a direction of a Z-axis along which weight 64 and mount substrate 61 are arranged.
For instance, if weight 64 moves along the Z-axis to move electrodes 66 away from each other, the capacitance between opposed electrodes 66 decreases. Even if acceleration along an X-axis or a Y-axis is applied, weight 64 can hardly move along the X-axis or the Y-axis, accordingly changing the capacitance between opposed electrodes 66 due to the acceleration by a small amount. Acceleration sensor 5001 cannot detect the acceleration along the X-axis or the Y-axis accurately.
Patent Document 1: JP10-177034A